Skip to main content
Wolf-Rayet Star. By ESA/Hubble & NASA Acknowledgement: Judy Schmidt

Wolf-Rayet Star

Wolf-Rayet stars (often referred to as WR stars) are a heterogeneous set of stars with unusual spectra showing prominent broad emission lines of highly ionised helium and nitrogen or carbon. The spectra indicate very high surface temperatures of 30,000 – 200,000 Kelvin, surface enhancement of heavy elements, and strong stellar winds.

Read More

Giant Star. By Oona Räisänen (Mysid)

Giant Star

A giant star is a star with substantially larger radius and luminosity than a main-sequence (or dwarf) star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzsprung-Russell diagram and correspond to luminosity classes II and III. The terms giant and dwarf were coined for stars of quite different luminosity despite similar temperature or spectral type by Ejnar Hertzsprung about 1905.Read More

T-Tauri Star. By ESO/L. Calçada - ESO

T Tauri Star

T Tauri stars (TTS) are a class of variable stars named after their prototype – T Tauri. They are found near molecular clouds and identified by their optical variability and strong chromospheric lines. T Tauri stars are pre-main-sequence stars in the process of contracting to the main sequence along the Hayashi track, a luminosity-temperature relationship obeyed by infant stars of less than 3 solar masses in the pre-main-sequence phase of stellar evolution.Read More

Protostar. By NASA/JPL-Caltech


A protostar is a very young star that is still gathering mass from its parent molecular cloud. The protostellar phase is the earliest one in the process of stellar evolution. For a one solar-mass star it lasts about 1,000,000 years. The phase begins when a molecular cloud first collapses under the force of self-gravity. It ends when the protostar blows back the infalling gas and is revealed as an optically visible pre-main-sequence star, which later contracts to become a main sequence star.Read More

Stellar Classification. By LucasVB

Stellar Classification

In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Showing the relationship between the stars’ luminosities versus their spectral classifications is done in the Hertzsprung-Russell diagram. The spectral class of a star is a short code summarizing the ionization state, giving an objective measure of the photosphere’s temperature and density.Read More